We develops a finite-difference time-domain (FDTD) code suitable for modeling borehole radar measurement. Transmitting and receiving antennas are modeled exactly by using sub-grid technique while the antenna equivalent circuits are considered for transmitter and receiver. Borehole radar responses to several mineral bodies are simulated numerically and analyzed. It is found that the radar responses are affected by not only the locations but also the orientation of mineral bodies. When the ore is symmetry like a point target, the radar signals look like a hyperbola. But for a planar vein with certain size and geometry, the radar signals are complex. Although the natural existence of the mineral bodies is diverse, these simulations could still provide us some insights into the capability of borehole radar detection.